There is a so-called electric power steering (EPS) device that assists steering using a steering assist motor in order to reduce a vehicle steering force in so-called automobiles such as passenger cars and trucks. In the EPS device, a driving force of a steering assist motor is applied, as an assist force, to a steering shaft or a rack shaft by a transmission mechanism, which is a gear, a belt, or the like, via a speed reducer. For the purpose of enabling a steering angle ratio, which is a ratio of a steering angle of a steering wheel and a steered angle of a drive wheel, to be variably controlled and lowering a risk of a collision with an object around the vehicle in such an EPS device, a technique of changing the steering angle ratio in accordance with a distance from the object, a relative speed, and a distance until reaching the object is disclosed (for example, see Patent Literature 1).